Adsorption process



2,930,447 Ansonrr osr rnocuss Richard lvLBarrer, Brantley, England, assignor to-Union Carbide Corporation, a corporation of New York No Drawing. Applicationduly 29, 1955 Serial No. 525,380

3 Claims. .(Cl. 183-=-114.-2)

' This invention relates to a process whereby the adsorptive properties of a molecular sieve are advantageously l modified and to a process foreilecting the separation of=a mixture of molecules using the modified molecular sieve.

Molecular sieves, for example certain zeolites, exhibit.

adsorptive properties that permit their use in, separating mixtures of fluids. Under the proper circumstances the molecular sieve will preferentially or selectively adsorb one constituent of the fluid mixture and reduce its concentration in or completely remove it from the mixture. The preference of a molecular sieve for one material in 1a mixture is affected by a'number of factors including'the size and polarity of the molecules in the mixture. Not all molecular sieves exhibit the same preferences nor do they have the same capacities. Thus, the choice of a molecular sieve having the desired properties for agive separation is a matter of prime importance. I

It is the object of the preventinvention to'providem process for the modification of the adsorptive properties of a molecular sieve. Another object of the invention'is to provide a process for the modification of the properties of a'molecular sieve whereby the preference of the sieve v for adsorbate molecules is altered.

Naturally occurring molecular sieves contain adsorbed Water as do the synthetic molecular sieves whichare prepared from aqueous solutions of reactants. Before the molecular sieves can be used as adsorbents a part at least of this adsorbed water must be removed.

It has now been discovered that the adsorptive c'haracs teristics 'ofa molecular sieve can be alteredbydntroducinginto thedehydrated molecular sieve a quantity of a non-aqueous or "dehydrated polar adsorbate. 'Particucrystals increases.

emitted M as, 19 0 .From the datain TableLit can'be clearly seen that the capacity of the mordenite' crystalsforoxy gen and hydromethylamine in the gen decreases as a the .amount of I In another series of tests the effect of adsorbed ammoniaton'the selectivity of chabazite crystals was investigated. The chabazite was activated or dehydrated :b y

heating it for 48 hours at about 450- C. .in .a vacuum of upp-to-lx-w mm. of.-mercu'ry.; Ammonia was-.introduceid into the chabazite and the effect of 'theam'ountiof I adsorbed ammonia on the adsorptive properties of the crystals for oxygen, argon,.andnitrogen at .l8:3 "-C. and

I 650 mm. of mercury was observed. .Thedata obtained 'larlygood results haveb'een obtained using-ammonia and E 1 modifying polar absorbate. The effect'of the presence-of such a polar adsorbate in a molecular sieveis determined 1 to an extent by the sizeof the openings in the molecular 't ammonia derivatives, for example methylamine, as the v 'mordenite and chabazite. synthetic molecular sieves, designated Zeolite and Zeolite A, have hadtheinadsorptive propertiesmodified and have been used to eliect pacity as the result of their partial saturation with a polar adsorbate according to the teachings of the invention. The discovery that the properties of molecular sieves can be altered as indicated above permits the use of a given molecular sieve in a wider range of adsorption processes. I The process of the invention is illustrated by the treatmerit of mordenite, a naturally occurring zeolite-.-- Crystals of mordenite were freed of water and otheradsorbed gasesby heating them in vacuo 'at 400 C. for about- 48 hours. Measured amounts of methylamine were then adsorbed on the crystals.

. cury pressure and l83 C. was determined. The-data from these tests are presented in Table I. In the table the.

amount of adsorbate adsorbed isgiven in the grams of adsorbate per gram of mordenite,

Thecapacity of the treated crystals for oxygen and hydrogen. at 650 mm. of merof ads'or'bate 'per gram of 'c'haba'zite.

during these tests are compiled in Table H. In the table the amounts of adsorbate adsorbed are. given as the grams The adsorptive capacity of chabazite for ammonia at 183 C. and 650 mm. of mercury is 0.18 gram of ammonia per gram of (:habazite. From this and the data it can be seen, for examplep-thatwhen the adsorptive 7 capacity of the crystals foroxygen is reduced to 0.036 l i while the'amm'onia adsorbed'is 0.07 6, there'isa substan-f tial amount of pore volume remaining in the crystals.

.Inaddition to the naturally occurring moleculansicves,

separations of mixtures of molecules according to the invention. a a 7 Zeolite X-may be made according'to the procedureadescribed in UnitedStates patent application Serial ;No.'

400,389, .filed December 24, 1953, .now 11.8. :Patent bio. 2,882,244, issued .April :14, 19.59. Thecomposition of Zeolite may be represented as a I A typical composition for the sodium form of Zeolite X L may be represented as The majorix ray diffraction lines of a isamplezottcrzystal line zeolite X, including the sodium form thereof, are given in Table A:

TABLE A d value of reflection in A.

In obtaining the X-ray diffraction powder patterns, standard techniques were employed. The radiation was the Km doublet of copper, and a Geiger counter spectrometer with a strip chart pen recorder was used. The peak heights, I, and the positions as a function of 2 6, where 0 is the Bragg angle, were read from the spectrometer chart. From these, d(obs), the interplanar spacing in A. corresponding to the recorded lines was calculated. The X-ray patterns indicate a cubic unit cell of dimensions between 24.5 A. and 25.5 A.

Zeolite A may be made according to the procedures described in United States patent application Serial No.

400,388, filed December 24, 1953, now U. 5. Patent No. 2,882,243 issued April 14, 1959. The composition of zeolite A may be represented as In this formula M represents a cation and n its valence. A typical composition for the sodium form of zeolite A may be represented as 0.99 M 0 10 A1 0 1.85 SiO 5.1 H 0 The major lines of the X-ray diffraction pattern of AhOa: 1.85i:0.5 SiO:: 0 to 6 H2O zeolite A are shown in Table B. These lines were ob-,

taincd using the same techniques employed with respect to the data shown in Table A.

TABLE B d value of reflection in A.

adsorbed by the crystals. The measurements were made at 183 C. and 700 mm. of mercury.

TABLE III Amount of Amount of Hi Oxy oppp 0C0 accrue pea-F5 OQNOO From the data in Table III it can beseen that small amounts of ammonia greatly reduce the capacity of the crystals of sodium zeolite A for oxygen. This permits the use of sodium A zeolite in separations wherein the rejection of oxygen by the adsorbent is desired.

The elfect of a non-aqueous non-polar adsorbate on a molecular sieve having a relatively open structure is demonstrated by the data in Table IV. In the table the capacity of sodium zeolite X for neopentane or tri-nbutylamine in the presence of various amounts of benzene appears. The amounts of adsorbed material are given as grams or milliliters of adsorbate per gram of adsorbent (designated g./g. and ml./g. respectively). The data involving the neopentane was obtained at 25 C. and 700 mm. of mercury pressure while the data involving tri-n butylamine was obtained at 25 C. and 1 mm. of mercury pressure.

It can be seen from the data in Table IV that with sodium zeol-ite X the presence of one dehydrated nonpolar adsorbate in the crystal does not alter the selectivity of the crystal but merely subtracts from the available pore space in the crystal.

Molecular sieves modified according to the teachings of the invention may be used to separate mixtures of molecules. For example the data in Table II relating to chabazite shows that as the amount of ammonia in the crystal is increased the capacity of the crystal for nitrogen is decreased to a greater extent than is the capacity of the crystal for oxygen. Thus the modified crystal can be used advantageously to efiect a separation of oxygen and nitrogen by preferentially adsorbing oxygen. 7

What is claimed is:

1. A process for the resolution of a mixture of oxygen and nitrogen by preferential adsorption of oxygen on dehydrated chabazite which comprises providing a quantity of dehydrated chabazite, adsorbing on said chabazite ammonia in an amount less than the capacity of said chabazite for ammonia to increase the relative capacity of said chabazite for oxygen, and thereafter contacting a said mixture with said modified chabazite and selectively adsorbing on said chabazite the oxygen in said mixture.

2. A process for the resolution of a mixture of oxygen and argon by preferential adsorption of oxygen on dehydrated'chabazite which comprises: providing a quantity .of dehydrated chabazite, adsorbing on saidchabazite ammonia in an amount greater than 0.061 gram of ammonia per gram of chabazite and less than the capacity of said chabazite for ammonia to increase the relative capacity of said chabazite for oxygen, and thereafter contacting said mixture with said modified chabazite and selectively adsorbing on said chabazite the oxygen in said mixture.

3. .A process for the resolution'of a mixture of oxygen and hydrogen by preferential adsorption of hydrogen on dehydrated mordenite which comprises providing a quantity of dehydrated mordenite, adsorbing on said mordenite methylamine in an amount greater than about 0.0276 gram of methylarnine per gram of mordenite and less than the capacity of said mordenite for methylamine to increase the relative capacity of mordenite for hydrogen; and thereafter contacting said mixture with said modi- 5 V 5 fied mordenite and se1ec tive1y adsorbing on said mordenite OTHER. REFERENCES the hydrogen m Sald mlxmre' Separation of Mixtures Using Zeolites in Molecular References Cited in the file of this patent iii 2 g g g g f Chem' Ind! "9 UNITED STATES PATENTS 5 Sorption by Gmelinite and Mordenite, by R. M.

1,443,220 Guye et a1. Jan. 23, 1923 Barter, Trans Faraday Soc., volume 40 (1944), pages 2,254,799 Erdmann Sept. 2, 1941 555-564. 

1. A PROCESS FOR THE RESOLUTION OF A MIXTURE OF OXYGEN AND NITROGEN BY PREFERENTIAL ADSORPTION OF OXYGEN ON DEHYDRATED CHABAZITE WHICH COMPRISES PROVIDING A QUANTITY OF DEHYDRATED CHABAZITE, ABSORBING ON SAID CHABAZITE AMMONIA IN AN AMOUNT LESS THAN THE CAPACITY OF SAID CHABAZITE FOR AMMONIA TO INCREASE THE RELATIVE CAPACITY OF SAID CHABAZITE FOR OXYGEN, AND THEREAFTER CONTACTING SAID MIXTURE WITH SAID MODIFIED CHABAZITE AND SELECTIVELY ADSORBING ON SAID CHABAZITE THE OXYGEN IN SAID MIXTURE. 